Stability criterion for large bipolarons in a polaron-gas background

In this paper we consider the stability of a large bipolaron embedded in a polaron gas. The main conclusion is that an isolated nonstable bipolaron can be stabilized in the presence of a polaron gas exhibiting Fermi statistics. On the other hand, the exchange interaction tends to destabilize the bipolaron. This study has been performed both for bulk three-dimensional materials and for thin two-dimensional films using the Hartree-Fock approximation. The bipolaron has been described by an extension of the Feynman polaron model.